All aboard the lobster train

Spiny lobsters, Panulirus argus, have an unusual and poorly understood migratory behavior. Every autumn, many of the shallow living lobsters around the Bahamas begin forming traveling queues that aggregate into long chains of marching lobsters. These chains can swell to thousands of individuals as the animals migrate to deeper waters.

Our main man, David Attenborough, breaks it down and somehow manages to make a skittering train of lobsters feel epic:

As mentioned in the video, the migration possibly occurs in order for the lobsters to escape turbulence and turbidity in the shallows resulting from autumn storms that sweep into the Bahamas. The migration has long been observed in tight correlation with these storms. Following the first storm of the year, the spiny lobsters begin amassing at buildup areas and prior to embarking on the mass migration. The cue to begin queueing (hah) is likely the sharp water temperature drop following the first storm. Indeed, in laboratory observations, decreases in water temperature increased queueing among captive spiny lobsters.

The purpose of the lobster queue formation during migration is likely twofold. For one, traveling in a line reduces water drag for the lobsters traveling behind others. To borrow a term from racing, the lobsters are drafting on the wakes of their line-mates. In this manner, the lobsters conserver energy and momentum on their trek. The other reason for forming the migration queues is likely predator defense. Beyond projecting increased size via aggregation, the lobster queues can rearrange into a defensive circle to cover their vulnerable back-sides. You can see an example of the onset of defensive formations in the photo below.

Panulirus argus migratory train. The lobsters at the front of this train were perturbed by the divers, causing them loop back into the train, creating a lobster vortex. Adapted from Kanciruk and Herrnking, 1978.

There are also fairly numerous fossils of Ampyx (Lonchodomas) trilobites from the Ordovician of Morocco that have them lined up single file, head to tail. I haven’t seen any as long as that Cambrian train, but have seen some 8 trilobites long.

BTW, I only just found this blog. Mantis shrimp are my favourite extant invertebrates, so I’ll be bookmarking it and following along.

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